Number of tiers

Elections in Africa: A Data Handbook, 1999

Dieter Nohlen, Michael Krennerich and Bernard Thibaut

pp896-897 accessed via Google Books

IPU Election Archive reports

1994: http://www.ipu.org/parline-e/reports/arc/2315_94.htm

1999: http://www.ipu.org/parline-e/reports/arc/2315_99.htm